The invention relates to a traction device for improving traction of wheels, and in particular to a light to medium duty traction device for extending as a endless track between a pair of tandem mounted, powered, rubber tired wheels.
It is well known to enclose a single rubber tire with a link chain traction device for improving traction in adverse conditions, such as snow or mud. Such traction devices are characterized by two parallel lengths of conventional link chain which are interconnected by short lengths of link chain to provide a plurality of transversely disposed link chain tread portions for engaging a tread portion of the tire. Opposite ends of the lengths of chain are releasably interconnected to provide two generally similar loops of peripheral chain, interconnected by the transversely disposed tread portion chains.
It is also known to provide two parallel lengths of link chain interconnected by generally rigid cross members, the cross members being shaped, if desired, to conform generally to a cross section or profile of the tire. Such traction devices have sufficient length to pass around at least one pair of tandem mounted tires of a relatively light, rubber tired utility vehicle, so as to provide an endless crawler track. This track functions similarly to the well known heavy duty, interfitting pinned links of crawler tracks commonly associated with full size, heavy duty earth moving tractors etc. In general, rubber tired utility vehicles are more appropriate for medium to light duty earth moving work, snow clearing or other relatively light industrial activity, and in poor traction conditions where normal rubber tires do not provide sufficient traction or floatation, it is usual to fit endless chain traction devices as above described.
Typical link chain traction devices are shown in U.S. Pat. Nos. 1,446,870 (Borst) and 4,232,753 (Carlson), British Patent 411,083 (Vinsot), and Swedish Patent Publication 7802769-9 (Stalberg). The above U.S. and British patents disclose traction devices having a pair of transversely spaced apart lengths of link chains, each length comprising a plurality of interconnected similar links, with rigid cross members extending between regularly spaced particular links of the chain, the particular links being identical to the remaining links. Borst and Vinsot disclose various means to connect ends of the cross members to the particular links, e.g. bolts or cotter pins, such means being time consuming to assemble manually and resulting also in a relatively complex and costly connection. Carlson discloses cross members with end portions having slots or recesses to receive the particular links which are welded to the cross members. Such connections appear to be prone to premature failure due to high stresses associated with the connection, particularly if the connection is rigid and extends a significant distance on either side of the cross member. Stalberg discloses an elongated open-sided hook of flat bar which has separate ends welded to the cross member, the separate ends extending rigidly a considerable distance on either side of the cross member. In applicant's opinion, if the particular mechanical connection of the chain to the cross member is exceptionally long when compared with adjacent links of the chain, as in the Swedish and British patent publications, or when compared to radius of the tire to which the traction device is fitted, high stresses can be developed which can cause failure of the connection between the link and the cross member. In addition, a link that is relatively long when compared with width of the cross member prevents the traction device from being rolled up for storage in a compact manner, thus requiring additional storage space.
In addition, if the cross members are relatively wide compared to the radius of the tire, and connected together with limited rotation therebetween, there is a tendency for stones or rocks to be trapped between one or more cross members and the tire as the cross members are brought into engagement with the tire. A stone trapped between the cross member and the tire can severely damage the tire, often causing puncturing. Alternatively the stone can be temporarily caught by the cross member, and then thrown from the tire as the tire revolves, risking injury to persons nearby.